In commonly assigned U.S. Pat. Nos. 4,933,780 and 5,016,030, a photographic filmstrip having a virtually transparent, magnetic film layer on the non-emulsion side of the filmstrip (referred to as an MOF layer) is disclosed in conjunction with various camera systems. One or more longitudinal read/write tracks are illustrated in the MOF layer between the side edges of the image frame area and the filmstrip information such as film type, film speed, film exposure information and information relevant to the processing and subsequent use (e.g., printing) of the exposed image frames is imprinted during manufacture of the filmstrip cartridge. The cameras disclosed therein provide for reading and/or recording of information on these tracks during camera use. The information recorded during camera use may include voiced messages or sound associated with the photographed scene and may be recorded in digital or analog format on certain of the tracks. It is contemplated that both the pre-recorded and any camera user recorded information will be read out for control and reprint purposes during photofinishing.
Commonly assigned U.S. Pat. Nos. 5,034,836, 5,041,933, 5,274,522, 5,285,324 and 5,285,325 and further U.S. Pat. No. 5,307,100 disclose magnetic recording head configurations for use in recording in longitudinal tracks alongside the filmstrip edges but not in the image frame area. These patents showing magnetic recording heads along the edges of the filmstrip outside the image area generally teach providing pressure pad supports or rollers on the emulsion side opposite from the recording heads and continuous motion of the recording medium to ensure reliable compliance for recording and/or reproducing information.
Reading and writing or recording information on tracks of a magnetic coating or stripe of a MOF layer is complicated by the low magnetic density of the semi-transparent magnetic film layer, the need to avoid damage to the filmstrip and the MOF layer, and the characteristics of the photographic filmstrip base and emulsion layers, the need to maintain alignment of the magnetic heads with the edge tracks and, in a still camera, the need for low cost, miniaturization and battery energy conservation.
Photographic film is of much greater thickness than the magnetic tape used for commercial and consumer recording and reproduction and is neither compliant nor inherently flat. When removed from its cartridge, a filmstrip shows a relatively high stiffness and very observable cross-curvature across its width that is convex on the non-emulsion side of the film. Further, the unwrapped filmstrip also shows a convex curvature along its length, again on the non-emulsion side of the film. This latter curvature is attributed primarily to a core-set curl that results from the filmstrip having been tightly wound on a film cartridge spool.
The cross-film curvature across the width of the filmstrip is primarily caused by the number of multilayers of emulsion and MOF layer (if present). The emulsion multilayers (and MOF layer, if present) have different stretch properties than that of the base film substrate of acetate, PET, or PEN material. The cross-film curvature is also influenced by the bending phenomena known as anticlastic curvature. The degree of cross-film curvature also depends on environmental conditions, including the time and temperature history of the film, the relative humidity, and the thickness of the film. Because of the cross-curvature, it is difficult to achieve good contact or compliance across the width of a wide, multi-head array. To provide a reliable read or write signal, the magnetic recording head must remain in close proximity to the magnetic coating. Any disturbances, such as variations in film curl, can vary the relationship of the recording head to the magnetic coating and decrease the reliability of the signal.
In addition, the location of the side edge tracks is typically between image frame related sprocket holes or perforations which cause localized distortion of the filmstrip curl. In the photofinishing context, filmstrips may be spliced together, and the spliced ends may be laterally offset. The magnetic head suspension assemblies of the '836, '933, '324 and '325 patents are intended to accommodate the cross-film curvature, perforation disturbances, and splicing and other edge irregularities by allowing rotatable an/or lateral movement of the head element(s) and, in some cases, relative movement of the head elements with respect to one another.
Certain of these head suspension assemblies also employ a backer element to bear against the emulsion side of the filmstrip opposite to the magnetic head region of contact with the MOF layer to achieve sufficient compliance for recording and reproducing. In the '325 patent, reference is made to the '324 patent and a spring loaded biasing means or backer device for exerting force on the emulsion side to bias the MOF layer of the filmstrip against the magnetic read/write head. Other backer devices are disclosed in the '522, '030 and '100 patents, for example.
Backer plates, rollers, pads and the like are well known in the magnetic recording field for obtaining sufficient compliance of the magnetic media to the read/write head. Alternative means for biasing a magnetic recording web substantially into contact with a magnetic reading and/or recording element include resilient pressure pads and/or leaf springs. Representative of prior art in this instance are U.S. Pat. No. 3,984,049 issued Oct. 5, 1976 to Shawen and U.S. Pat. No. 4,780,782 issued Oct. 25, 1988 to Bordignon. The '049 patent discloses resilient pads which are positioned to be formed in a curved manner between a double curved leaf spring and a stationary frame. The leaf spring bows out and bears against one side of a magnetic web or tape in two locations to urge the other side of the tape against a magnetic read head and a magnetic recording head spaced along the length of the magnetic tape. The leaf spring ends and center point are secured to the stationary frame so that only limited deflection of the centers of curvature of the two bowed out sections are possible depending on the spacing of the fixed magnetic heads and the thickness of the tape or other media.
The '782 patent discloses a leaf spring or reed element which engages a magnetic tape and presses the tape toward a magnetic read/write head when the magnetic read/write head is moved from a retracted position into a position to read/write position. The leaf spring is shaped to conform in the working portion thereof as closely as possible to the curved shape of the head when it is advanced. The middle zone of the working portion is weakened by cut-outs or the like in order to reduce the pressure that, it is asserted, would otherwise be too high at the centrally located head gap.
In magnetic tape recording, the compliance between the read/write head gap and the magnetic coating is simplified by the density of the magnetic coating and the flexibility of the tape. Spacing between the head gap and the magnetic layer due to loss of compliance can be tolerated. Consequently, the reduction in compliance and spacing of the magnetic tape from the head gap proposed in the '782 patent to free up the tape transport may be tolerated for high density magnetic tape.
However, in the photographic filmstrip bearing the MOF layer described above, the density of the virtually transparent magnetic layer is considerably lower, and the film base and emulsion layer are less flexible than magnetic tape base. The handling characteristics of such a filmstrip require magnetic read/write head suspension allowing a differing degree of freedom of movement in order to accurately align with the MOF layer tracks, particularly along the filmstrip edge tracks.
Because of the low magnetic density of the MOF layer and the susceptibility of the emulsion side to scratching and damage, it is of particular importance that the read/write head-to-film interface must have high compliance and avoid scratching the MOF layer or the emulsion layers. As a result, extreme care must be taken in the design of the components of the interface to ensure that a minimum of surface damage occurs at the magnetic head interface and any load supporting member on the emulsion side of the film. Continued improvement in this area remains highly desirable.